1. Field of the Invention
The present invention relates to a method for modeling the pore-size distribution of a porous sample of variable porosity allowing achievement of laboratory studies on the behavior of the medium modeled in relation to fluids.
2. Description of the Prior Art
A porous medium is made up of a solid structure (or matrix) comprising cavities or pores connected with each other by channels or which are isolated from each other. The pores can be empty or saturated with one or more fluids. There can be for example porous rocks such as sandstones or limestones containing fluids in the pores, notably hydrocarbons. These reservoir rocks can be defined with precision from specific physical quantities such as the porosity, the permeability, i.e. the aptitude for allowing circulation of fluids which they are saturated with, the wettability, the geometry and the connectivity of the pores, etc.
The porous rocks that are found in oil-bearing reservoirs notably have a heterogeneous structure with alternation of zones exhibiting a greater or lesser porosity and permeability. Heterogeneities appear in the form of strata or nodules on the reservoir scale. On the microscopic scale, the porous media exhibit a fractal structure which is translated into a continuous pore-size distribution.
U.S Pat. No. 4,882,763 describes a process for constructing a model representative of a porous medium consisting mainly in etching onto glass a network of pores whose configuration reproduces that of the pores of a porous rock. Transposition is achieved by forming a digitized image of the network of pores by projection of light through a thin section of rock, that is reproduced on the glass substrate by means of a photolithographic process with chemical attack.
The minimum diameter of the channels realizable with a photolithographic process with chemical attack is of the order of 0.15 mm, which limits the variety of channel sizes available. Furthermore, the depth of the channels is not very regular over the total width thereof and it is limited in practice to 0.2 mm. In practice, the width of the channels thus realized is greater than their depth. Consequently, when liquid is injected into the network, the capillary pressure is imposed by the thickness of the channels and not by the width thereof, as it would be desirable for the physical model to be really representative.